Tensile behaviour of hybrid fibre architectures of randomly oriented strands combined with laminate groups

In this work, the tensile behaviour of co-moulded hybrid fibre architectures of randomly oriented strands (carbon/PEEK) combined with laminate groups (cross-ply, angle-ply and quasi-isotropic) is studied. The effects of varying the thickness of the laminate group relative to that of randomly oriented strands, stacking sequence of the architectures within a hybrid specimen, and the ply stacking sequences within the laminate group are quantified. Processing benefits of hybridization such as reduction in warpage and strand waviness are discussed. The tensile behaviour of hybrid fibre architectures is quantified and compared with that of randomly oriented strand specimens, base laminate groups and aluminum 7075. In addition, tensile failure modes have been investigated. Significant improvements in the mechanical properties of randomly oriented strands are observed with small proportions of laminate groups in the specimen. In addition, hybrid fibre architectures exhibit a positive synergy or a positive deviation from the rule-of-mixtures in the overall stiffness and strength behaviour when stacked in specific configurations, despite the same fundamental fibre type and matrix system. </jats:p

A Study of the Effect of Geometry Changes on the Structural Stiffness of a Composite D-Spar

The paper examines the impact of varying two geometric cross-section parameters of an advance composite D-spar on its structural stiffness. For a given blade topology, the orientation of the D-spar web with respect to the beam axis and the distance of the D-spar web from the leading edge of the blade have been selected here as the variables of study, as they govern the elastic properties of the composite cross-section. A code has been developed to calculate the matrix terms of the Euler-Bernoulli cross-sectional stiffness utilizing the closed form expressions of the structural properties formulated by assuming both Thin-Walled composite Beam theory (TWB) and Classical Laminate Theory. The code has been validated through the Variational Asymptotic Beam Sectional analysis (VABS) for the cross-sectional stiffness matrix. Two cases have been studied for a quasi-isotropic laminate D-spar. The first is for a symmetric airfoil, whereas the second is for an unsymmetrical airfoil. The variation of the stiffness parameters for the quasi-isotropic D-spar including the coupling parameters has been visualized into parametric maps. The paper also examines the impact that these geometric variables have on the stiffness-to-mass ratio to show that along with the ply orientations they play a major role in the aeroelastic tailoring and structural optimization of a composite blade.</jats:p

Multi-objective optimization of a composite rotor blade cross-section

This paper deals with the optimization of the ply angles and the internal geometry of a composite helicopter blade with a D-spar internal construction. The design involves the simultaneous optimization of several conflicting objectives such as: attaining three stiffness parameters, minimizing the blade mass and the distance between the mass-center and the aerodynamic-center. Optimization methods with a priori and a posteriori articulation of preferences are used to solve the problem. Among the a priori approaches, the min–max approach is used to transform multiple objective functions into a single criterion which is optimized with Particle Swarm Optimization (PSO). Alternatively, the design problem is tackled using a posteriori approach by using our in-house Non-dominated Sorting Hybrid Algorithm (NSHA)